Subcutaneous and intramuscular delivery of medicaments by injection are common in the medical arts. Examples of medical conditions that require frequent injections include diabetes, female infertility, AIDS, treatment of growth retardation in children, hepatitis, multiple sclerosis, migraine headaches, and allergic reactions. Traditionally, the medication for these and other ailments has been injected via a needle that punctures the skin of the patient. In many of these instances, the parenteral drugs are self-administered. For self-administered drugs it is particularly desirable that the injection be easily accomplished. Further, for circumstances requiring inoculations of a large number of persons, such as is often the case in the military services, it is also desirable that the inoculations be accomplished easily.
Despite the availability of fine gauge needles, many patients dislike needle injections due to pain, fear, and nervousness over needles. Additionally, practice has indicated there are serious risks related to needle injections. For example, blood-borne pathogens, such as HIV and hepatitis, can be transmitted to health care workers by accidental needle-sticks. Specific environments which have an exceptionally high risk of accidental needle-sticks include emergency rooms, county hospitals, and sites of mass immunizations. From these sources, hundreds of thousands of accidental needle-sticks are reported annually in the United States. The consequence is billions of dollars in annual costs due to the treatment of medical complications, testing and other related costs. Additionally, needle injections generate costs associated with the regulatorily required disposal of biohazardous sharps. For all of these reasons, there is a need for needle-free injection systems.
In efforts to minimize the fears, risks, and costs associated with needle injections, several types of needle-free jet injectors have been developed. Typically, such jet injectors expel all of their fluid medicament in a stream that is directed at a very high velocity. This high velocity stream accomplishes two tasks. First, due to its high velocity, the stream of fluid medicament is able to pierce a hole in the skin of the patient. Secondly, the stream injects the medicament through the hole into the patient.
Practice has indicated that existing needle-free jet injectors have several shortcomings. Most significantly, existing jet injectors have proven to be somewhat unsatisfactory due to side effects such as pain, bruising, and lacerations. These problems with existing injectors are largely caused by the high velocity at which the medicament is expelled into the patient throughout the injection process. Additionally, the strong contact that is required between the jet injector and the skin can contribute to bruising. Furthermore, movement of the injector during the injection process can cause lacerations. Also, with existing jet injectors, the high velocity at which the medicament is infused often causes undesirable painful enlargement of the hole in the skin of the patient during infusion of the medicament. In sum, practice has indicated that many patients desire a less painful injection than is currently available with existing jet injectors.
In addition to the difficulties noted above, the high velocity at which a medicament is infused by present jet injectors can also result in imprecise regulation of the depth of penetration of the medicament. For some patients this means the delivery of medicament may be directed into muscle tissue rather than into the subcutaneous tissue. If so, this may be undesirable if it leads to unpredictable drug absorption kinetics. Further, existing jet injectors have also proven to be inadequate due to incidents of incomplete drug delivery, and difficulty of use. In particular, incomplete drug delivery is often associated with uneven pressure between the skin and the injector during the injection.
Existing jet injectors with reusable syringes have additional shortcomings. For example, transmission of blood-borne pathogens is a risk associated with reusable syringes. Further, periodic disinfection of reusable syringes is an inconvenient necessity.
In light of the above, it is an object of the present invention to provide a needle-free medicament jet injector. Another object of the present invention is to provide a jet injector that administers an injection with minimal pain to the patient. Still another object of the present invention is to provide a jet injector that infuses the medicament into the patient at a lower velocity than existing jet injectors, so as to prevent harmful compression and damage to tissue, as well as to control the depth of the injection. It is still another object of the present invention to provide a jet injector with a stable skin to syringe interface to maintain consistent pressure between the skin and the syringe, and to prevent movement of the syringe relative to skin at the injection site during the injection. Yet another object of the present invention is to provide a jet injector with a disposable, replaceable, single-use syringe. Yet another object of the present invention is to provide a fluid medicament jet injector which is relatively simple to manufacture, is relatively easy to use, and is comparatively cost effective.